1. Field of the Invention
The present invention relates to a laser device, in particularly to a vertical cavity surface emitting laser and a manufacturing method of the same.
2. Description of Related Art
Vertical cavity surface emitting laser (VCSEL) has a primary feature of emitting light in a direction substantially perpendicular to the top surface of the laser chip. VCSEL is formed to have multiple layer structure of the epitaxial layer stack by deposition method like metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) with other conventional semiconductor steps.
The epitaxial layer stack includes an active region as the light emitting region, and two distributed Bragg reflectors (DBRs) arranged at opposite sides of the active region. A laser resonant cavity is formed between the two distributed Bragg reflectors, for the two distributed Bragg reflectors reflect the light with specific wavelength generated from the active region. Consequently, the light is amplified in the laser resonant cavity. For obtaining better optoelectronic characteristics, a current confinement aperture is usually formed within the upper side distributed Bragg reflector to confine the path of electric current. Thus, the threshold current can be decreased and the efficiency of optoelectronic conversion can be increased.
The conventional method used for manufacturing the current confinement aperture includes ion doping and selective oxidation. The two methods both have their advantages and disadvantages. FIG. 1 shows a conventional VCSEL adopts both methods for confining electric current. The epitaxial layer stack 10 has not only an ion-doped confinement region 11, but also an oxidizing confinement region 12 over the ion-doped confinement region 11. The ion-doped confinement region 11 has a confinement aperture 110. The oxidized confinement region 12 also has a confinement aperture 120. The confinement aperture 120 of the oxidized confinement region 12 is aligned with the confinement aperture 110 of the ion-doped confinement region 11. The VCSEL has better electric current confinement and better spectrum properties.
In practical manufacturing of the VCSEL, two sets of semiconductor processes need to be performed on the epitaxial layer stack 10 for forming the ion-doped confinement region 11 and the oxidized confinement region 12. However, due to overlay misalignment in semiconductor processes, the confinement aperture 110 of ion-doped confinement region 11 is usually not perfectly aligned with the confinement aperture 120 of the oxidized confinement region 12. Any slightly misalignment can downgrade the electric current confinement properties and de-optimize the spectrum properties.